The invention relates to a guidance system on a machine, especially a machine tool, consisting of a twist-resistant, vibration damping support body, of concrete for example, and at least one body forming the guidance ways, which is fastened thereon or integrated therein and which by itself is not twist-resistant.
In a machine which generally transforms or transports goods with the aid of the input mechanical energy, the individual units of the machine are moved relative to one another by displacing them along the course of guides. In a machine tool, for example, the workpiece holding tools and tool holders, powered or not, saddles and cross slides, tailstock, steady rests, and the like are movable relative to one another or relative to the machine frame, so that within a range established by the size of the machine, each position of the individual units relative to one another can be reached at any time and as often as desired by a repeatable, precise movement of individual units in order to permit the desired machining of the workpieces. These movable units are displaced along ways which, for the defined movement of the movable units, are to be as close as possible to a certain geometrical figure, usually a straight line or a plane.
This can normally be achieved only by precision machining, such as grinding and scraping. The guidance ways consist usually of steel or gray cast iron, and in some cases they are made of naturally occurring, hard minerals such as marble, for example, and can be made either from the same material as the part of the machine that bears them or of some other material, and the ways and machine base can be made either in one piece or can be assembled from a plurality of parts. In addition to steel and gray iron, concrete and plastic laminates are also used as materials for the machine base. The base of machine tools must be stable enough to prevent or minimize deformations of the guidance paths by the forces occurring in the operation of the tools.
The materials used for making the guidance ways and, as described, in some cases for the machine base, have a number of undesirable properties:
The first forming of the metal materials does not as yet yield surfaces accurate enough for use as guidance ways. Consequently a complex machining of the guidance ways is needed, for example milling, grinding and scraping, in order to obtain a surface that comes close enough to the ideal geometrical surface. This machining is very expensive on account of the great deal of time it requires and the great number of rejects that result.
A controlled and precise movement of the movable units of the machine on the guidance ways without requiring excessive driving force is possible only if the friction between the guidance ways and the parts to be displaced thereon is kept as low as possible. The lubrication between the ways and the part by means of oil or other lubricants that is required for this purpose is nevertheless unable to overcome the high starting friction at the beginning of the relative movement and cannot prevent damage to the ways if the lubricant system fails, due to the poor frictional properties of steel and gray iron materials. The static friction, which in spite of lubrication is substantially higher than the dynamic friction in these materials, is undesirable, since it greatly interferes with frequent, short movements.
The great thermal expansion of the metal materials used constitutes a problem, because in the event of temperature changes the relative positions of the individual units of the machine can vary.
The elasticity of steel and gray iron is a disadvantage because in the event of repeated stress and relief, such as can occur in machining operations, vibrations can build up on the guidance ways and in the machine frame, which when transmitted to the individual units of the machine tool can have a negative influence on the dimensional accuracy and surface quality of the finished workpiece.
Another disadvantage is wear when these materials are used in the guidance ways, which results from excessively low hardness of the materials combined with the great stresses that occur, insufficient chemical resistance and poor low-lubrication running characteristics. In the actual operation of a machine tool it is hardly possible to entirely avoid the complete or partial failure of the lubrication system or the action of coolants and lubricants containing moisture or acid, and dirt particles, especially grinding dust, on the guidance ways.
Further reduction of the dimensions and hence also of the weight of the guidance ways and thus also of the machine is not possible, since they are defined by the ability of the materials to withstand pressure.
The invention is directed to the object of providing a machine of the kind described above with guidance ways which have the lowest possible thermal expansion and elasticity, are very hard, have good characteristics for running with low lubrication, and can be manufactured simply and very accurately.